As many people have said - with HTML5, you basically give your IP away and hope for the law to keep people honest. Making money is those conditions is the old open source conundrum.
I would suggest the OP to sell support contract (sponsored features, priority bug fixing, ...) to the Chinese customers of his copycat.
If the situation gets worse (eg: the chinese firm translate their website in English), the engine can be open sourced and try to recover with the support.
If the Chinese site is selling the minified/uncommented JS code that you would get from "view source" then he probably wouldn't be in business for long.
In this case, it sounds like he bought a copy of the engine/level editor/build scripts/documentation and is selling that. Is that any different than buying the Unreal Engine Source Code and reselling it for 50% off?
I would suggest the OP to sell support contract (sponsored features, priority bug fixing, ...) to the Chinese customers of his copycat. If the situation gets worse (eg: the chinese firm translate their website in English), the engine can be open sourced and try to recover with the support.